This invention relates to a sphere (ball) polishing machine which is suitable for polishing a precise steel ball superior in low vibration characteristic which is employed for instance for a ball bearing.
In general, a sphere polishing machine for forming steel balls which are applied, for instance, to a ball bearing employs a circular conveyor to supply balls which are to be polished (hereinafter referred to as "workpiece balls", when applicable) to a sphere polishing machine body for the mass production of spheres (balls).
The sphere polishing machine with the circular conveyor will be described with reference to FIG. 1. FIG. 1 is a diagram showing the whole arrangement of a conventional sphere polishing machine.
An shown in FIG. 1, the sphere polishing machine, comprises: a circular conveyor 7 accommodating a number of workpiece balls 3; and a machine body which polishes the workpiece ball 3 (supplied from the circular conveyor 7) precisely spherical. In the circular conveyor 7, a number of workpiece balls 3 in it is led to an outlet by the rotation of a moving section (not shown). The outlet is connected to a chute 7a through which a workpiece ball led to the inlet 4a the machine body. Furthermore, the circular conveyor 7 has a chute 7b through which a workpiece ball discharged through the outlet 4b of the machine body is led to the inlet of the circular conveyor 7.
The machine body comprises a stationary board 2; and a rotary board 1 which is a polishing body for workpiece balls 3 and rotates coaxially with respect to the stationary board 2 while being pushed against the stationary board 2 with a predetermined polishing force. In the inner face of the rotary board 1 which confronts with the stationary board 2, a plurality of grooves (not shown) for receiving workpiece balls 3 are coaxially formed. Each of the grooves is uniform and continuous in the circumferential direction, and its section is similar to the radius of curvature of the workpiece balls 3. Similarly, in the inner face of the stationary board 2 which confronts with the rotary board 1, a plurality of grooves 5 for receiving workpiece balls 3 are coaxially formed. Each of the grooves 5 is uniform and continuous in the circumferential direction, and its section is similar to the radius of curvature of the workpiece balls 3. The grooves 5 of the stationary board 2 are confronted with those of the rotary board to form ball passageways for workpiece balls 3.
The workpiece balls 3 supplied to the inlet 4a through the chute 7a from the circular conveyor 7, are allowed to go into the ball passageways in the order of supply. Each workpiece ball 3 is moved along the ball passageway while being rotated by the rotation of the rotary board 1 and the predetermined pressure applied thereto by the rotary board 1. During the movement, the part or parts of the workpiece ball 3 which are brought into contact with the guide groove of the rotary board are polished. Whenever the workpiece ball moves through the ball passageway, the workpiece ball is polished once. The workpiece ball thus polished is returned through the chute 7b into the circular conveyor 7.
The polishing operation is performed predetermined times that workpiece balls 3 are supplied from the circular conveyor 7 into the machine body, and are polished by the machine body, and are then returned to the circular conveyor 7. This polishing operation performed repeatedly polishes the workpiece balls so that the workpiece balls are precisely spherical.
With the above-described sphere polishing machine, during the movement of a workpiece ball the inclination of the rotating axis of the workpiece ball is hold substantially constant in angle. Hence, a surface polishing locus of a workpiece ball per polishing operation is extended in a certain direction and considerably small in width, and therefore it is difficult to uniformly polish the surface of a workpiece ball with one polishing operation. In order to uniformly polished the surface of a workpiece ball, it is necessary to increase the number of times of the above-described polishing operation, which lowers the polishing efficiency of workpiece balls.
In order to overcome the above-described difficulty, the following system has been proposed in the art: The section of each of the grooves formed in the rotary board is continuously changed in the circumferential direction of the rotary board so that, as a work piece ball is moved along the groove, the contact point of the workpiece ball with the groove is shifted (Japanese Patent Unexamined Publication No. Hei. 6-91506. More specifically, the section of each of the grooves formed in the rotary board is continuously changed in the circumferential direction, whereby during movement of the workpiece ball the contact angle of the workpiece ball with the groove of the rotary board is continuously changed so that the workpiece ball is slipped with respect to the rotary board and the stationary board. This slip results in a skew motion that the inclination of rotating axis of the workpiece ball is continuously changed, whereby the surface of the workpiece ball is substantially uniformly polished by one polishing operation.
In the above-described polishing system, the slip provided between a workpiece ball and the rotary board and the stationary board depends on the difference in frictional force which is provided between the workpiece ball and the rotary board and the stationary board. Hence, it is difficult to positively obtain a skew motion which is sufficient for only one polishing operation to substantially uniformly polish the surface of the workpiece ball; in other words, it is difficult for only one polish operation to substantially polishing the surface of the workpiece ball.